An instance of an ORB runs on each computer in a distributed system. When a request for a service that is provided on another system is processed by the ORB, it sets up an inter-ORB communication (Figure 1):
Figure 1 Inter-ORB communications
In this example, if object o1 or o2 requests a service from o3 or o4 then this requires the associated ORBs to communicate. A CORBA implementation supports ORB-to-ORB communication by providing all ORBs with access to IDL interface definitions and by implementing the OMG’s standards Generic Inter-ORB Protocol (GIOP). This protocol defines standard messages that ORBs can exchange to implement remote object invocation and information transfer. When combined with lower level Internet TCP/IP protocols, the GIOP allows ORBs to communicate across the Internet.